142 INFECTIOUS AND PARASITIC DISEASES. 



may be deposited upon them by the latter. Mosquitoes 

 belong to the two-winged flies or diptera, a fact which, 

 if previously unknown to the reader, will now suggest a 

 third way in which these insects are harmful, viz., 

 by acting as secondary hosts for other human parasites. 

 Because the relationship of mosquitoes to malaria, 

 yellow fever and filariasis, has already been sufficiently 

 elucidated, additional reference to them here would be 

 superfluous. 



Finally, diptera may accidentally convey disease- 

 agents either upon their bodies or in their feces, factors 

 in disease that have also already been considered else- 

 where. 



To the (Estridas or bot-flies belong those species 

 the larvae of which are parasitic upon man. 



Dermatobia noxialis Goudot. This fly 



GEsTRus is a common pest in tropical America. 



HoMiNis. Known under numerous names, viz., Ver 

 macaque (Cayenne and Mexico), Ura 

 (Brazil), Torcel (Costa Rica), its larvae are deposited 

 upon exposed portions of the body, whence they work 

 their way into the subcutaneous tissues. Here, if 

 undisturbed, they complete their growth and issue when 

 mature from the abscesses to which their presence gives 

 rise. The larvae are quite characteristic in that one 

 end (head) is quite large in comparison with the other, 

 and there are minute spines on segments two and 

 three. 



